To date, nine National Jewish patients have been studied as part of this GCRC protocol. After informed consent, patients took their prescribed antituberculosis medications under direct observation. A series of blood samples were collected through an intravenous catheter, and assayed using HPLC or GC. The assay results are being analyzed as part of a multicenter population pharmacokinetic study. The goal is to identify variables that affect the pharmacokinetics of these drugs in patients with tuberculosis, and to develop strategies to overcome these problems in the clinical setting.